Apparatus for the continuous production of chipboard or like material

ABSTRACT

Apparatus for the continuous production of boards such as chipboards, fibreboards and the like which includes an endless steel band guided on guiding and feeding rollers so as to convey board material to where it is compressed between the band and a rotatable pressing drum. In order to accurately control the temperature across the width of the drum and steel band, with a consequent maintenance of uniform thickness across the width of the board produced, a plurality of separate heat transfer elements are positioned adjacent the steel band and within the pressing drum. These heat transfer elements are spaced from one another in the direction of the width of the band and drum so as to accommodate a separate heating or cooling of the various sections across the width of the band and drum. Automatic thickness control means in the form of thickness detectors arranged across the width of the finished board and a control device for controlling the individual heat transfer elements in response to the detected thickness variations are also provided.

United States Patent 1191 Gersbeck et al.

[ June 24, 1975 1 1 APPARATUS FOR THE CONTINUOUS PRODUCTION OF CHIPBOARD OR LIKE MATERIAL [73] Assignees: Bison-werke Bahre and Greten GmbH and Co. KG, Springe/ Diester; Hermann Berstorff Maschinenbau GmbH, Hannover- Kleefeld, both of Germany 221 Filed: Oct. 9, 1973 211 Appl. No.: 404,387

[30,] Foreign Application Priority Data 3,039,137 6/1962 Smith et a1 425/83 3,726,627 4/1973 Gersbeck 425/371 3,782,875 l/l974 Olschewski "v25/273 Primary Examiner-Robert L. Spicer, Jr. Attorney, Agent, or Firm-Craig & Antonelli 5 7 ABSTRACT Apparatus for the continuous production of boardssuch as chipboards, fibreboards and the like which includes an endlesssteel band guided on guiding and feeding rollers so as to convey board material to where it is compressed between the band and a rotatable pressing drum. In order to accurately control the temperature across the width of the drum and steel band, with a consequent maintenance of uniform thickness across the width of the board produced, a plurality of separate heat transfer elements are positioned adjacent the steel band and within the pressing drum. These heat transfer elements are spaced from one another in the direction of the width of the band and drum so as to accommodate a separate heating or cooling of the various sections across the width of the band and drum. Automatic thickness control means in the form of thickness detectors arranged across the width of the finished board and a control device for controlling the individual heat transfer elements in response to the detected thickness variations are also provided.

32 Claims, 3 Drawing Figures APPARATUS FOR THE CONTINUOUS PRODUCTION OF CHIPBOARD OR LIKE MATERIAL BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to apparatus for the continuous production of chipboard or like material and which includes an endless band which is guided under tension so as to press the board material against a pressing surface. More particularly, the invention relates to apparatus of the above-mentioned type wherein the band is a heatable steel band which is guided around a plurality of guide and feed rollers as well as a heatable pressing drum. Apparatus of this general type is described in US. Pat. No. 2,890,484 and Holz-Zentralblatt 1970 No. 118, page 1726/77.

In a first of the known apparatus the guide and feed rollers for guiding the steel band and compressing the layer of chips or the like all have a relatively large diameter so that the whole apparatus takes up a relatively large amount of space. In the second of the known apparatus, only the roller serving to compress the layer of chips and constructed as a pressing drum has a relatively large diameter so that the space requirements of that apparatus are less than those of the first apparatus. The temperature necessary for hardening the layer of chips is applied in such a way that in the first apparatus all the guide and feed rollers are heated whereas in the second apparatus practically only the pressing drum was heated. As a result of the above-described temperature provisions the endless band which passes around the guide and feed rollers or the pressing drum is also heated at least in the vicinity of the actual pressing drum.

Chipboard produced on such continually operating presses generally has a thickness of 0.6 to 6.0 mm. Due to the limited thickness of these chipboards considerable importance is attached to the requirement that these chipboards should leave the apparatus without requiring subsequent grinding. Therefore it is required/desired that the continuously produced lengths of chipboard only have very small thickness tolerances.

Producing the small thickness difficulties has caused difficulties in prior arrangements because in particular the heated pressing drum in the vicinity of its edges radiates more heat than in the central area so that temperature differences of up to C occur across the width of the board as it is being formed between the drum and band. Because of these temperature tolerances, the central areas of the relatively long steel band and the pressing drum with a relatively large diameter expand to a greater extent than the edges. Due to the resulting relative shortening of the band in the edge regions, the band tension increases so that along its edges the layer of chips is compacted more strongly than in the central area and consequently chipboard which is not of uniform thickness is obtained. The smaller thickness of the chipboards in the region of its edges can lead to disadvantageous cracking or breaking of the chipboards during handling and during transportation.

The present invention contemplates overcoming the above-discussed disadvantages of prior arrangements by improving the known apparatus so that chipboard can be produced which not only will have a substantially constant cross-sectional thickness over the complete width but will also have a strength in the edge regions such that the tendency to cracking or breaking of parts of the board will be avoided or at least substan tially reduced.

Preferred embodiments contemplated by the present invention include apparatus for the continuous production of chipboard or like material comprising an endless, heatable steel band which is under tensior and is guided around a plurality of guide and feed rollers as well as a heatable pressing drum and including a plurality of parallel heating and/or cooling (heat transfer) elements arranged to influence the temperature of at least said steel band and whose temperatures are controllable in such a way that in operation a layer of chipboard forming material can be compressed to substantially the same thickness over its entire width. As a result of this zonal heating due to the separate temperature control of the heat transfer elements, not only the cross-sectional shape of the steel band, but if desired alsothe peripheralloutline of the pressing drum can be influenced in such a way that the cross-section of the finished chipboard will be substantially constant at all points. In a preferred embodiment of the invention we also provide parallel heating and/or cooling elements which serve, in use, to directly influence the pressing drum and the guide and feed rollers and which extend peripherally of the pressing drum and the guide and feed rollers, the temperature of said elements being controllable in such a way that a layer of chips can be compressed to substantially the same thickness over its complete width.

It is preferred to associate the heating and/or cooling elements with at least one length of the endless steel band located between the guide and feed rollers immediately upstream of the pressing portion of the travel path of the band. As a result the necessary temperature conditions can be precisely regulated by appropriately controlling the temperature of the respective separate heating and/or cooling elements spaced across the width of the band.

As regards heating the pressing drum it has been contemplated to heat not only the surface of the pressing drum but also the side walls thereof and to insulate the latter against radiation. The heating of the pressing drum surfaces can however be improved in accordance with another feature of the present invention by providing the side walls of the drum with openings through which the side walls of the drum are heatable or coolable with water, oil or the like or heatable by electrically heatable elements disposed in said openings. These openings are appropriately arranged in concentric circles around the axis of rotation of the pressing drum, the number of heating elements arranged near the cylindrical surface of the pressing drum preferably being larger than in the area closer to the axis. As a result the pressing drum temperature can be accurately regulated in the edge regions thereof.

These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an apparatus constructed according to the invention;

FIG. 2 is a view from below of a=prtion of the steel band of the FIG. 1 apparatus with a plurality of parallel heating and/or cooling elements arranged in accordance with the present invention; and

FIG. 3 is a cross-section through a portion of the pressing drum of the FIG. 1 apparatus with a plurality of heating and/or cooling elements arranged in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, an endless steel band 1 is guided around a plurality of guide and feed rollers 2, 3, 4, 5, 6 and a pressing drum 7 in such a way that glued chips 9 can be supplied to the steel band 1 by forming station 8 between the guide roller and a roller 6 constructed as a feed roller. The layer of chips 9 is fed in the direc tion of arrow 10 by the continuously moving band 1 to a gap 11' between feed roller 6 and drum 7 where it is compressed between drum 7 and band 1 As the steel band 1 passes around most of the periphery of drum 7 it is guided off the periphery of drum 7 via guide roller 2. The binder added to the layer of chips hardens during the pressing operation so that the finished web of chipboard 9 can be removed downstream of the guide roller 2 in any desired direction by means not illustrated. In the preferred embodiment shown in FIG. 1, roller 4 acts both as a guide means for the steel band 1 and as a feed roller which aids in pressing the steel band 1 against the periphery of pressing drum 7.

Beneath steel band 1 and between guide roller 5 and feed roller 6 are provided a plurality of heating and/or cooling elements l2, 13, 14, 15 and 16 (see FIG. 2) which permit the heating from below of steel band 1 in the desired manner. In the present context elements as used herein is understood to mean all heating or cooling elements which can serve for heating or cooling the steel band 1. In a similar mannen-(FIG. 2 is representative of spaced plural elements) a plurality of heating elements 17 are arranged between the feed rollers 4 and 6 and in addition further elements l8, 19, 20 and 21 are arranged between the other rollers. These other elements are provided in accordance with preferred embodiments of the invention either only on one side or on both sides of the steel band 1 in dependence on the desired amount of heating and/or cooling of the band,

The arrangementof heating or cooling elements inside the -drum 7 is shown in FIG. 3 in which circumferentially of the pressing drum 7 annular elements 22, 23, 24, 25 and. 26 are provided. It is not essential to have five such elements and for example, there need only be three annular elements and the same applies for the elements which act on the steel band 1.

The individual elements 22 to 26 are connected via wires 22a to 26a with sliding contacts 22b to 26b which control the temperature of the individual elements 22 to 26 via corresponding regulators of schematically indicated temperature controller C.

'It also falls within the scope of the invention to provide rollers 4, Sand 6 with annular elements around the inside of the said rollers in a manner similar to the above-described arrangement of FIG. 3 for the pressing drum 7.

It is further contemplated by the present invention to provide embodiments with both pressing drum 7 and guide or feed rollers 2 to 6 also heated with steam, water or oil. It is within the scope of the skilled expert to select the appropriate heating type given the present disclosure,

So that the basic concept of the invention will be fully understood it is first assumed that the chipboard 9 (FIG. 1) is thicker in the edge region than in the central region as detected by thickness sensing elements S. If now steel band 1 is cooled in its two edge regions (by appropriate control of the temperature by temperature controller C in the edge positioned heat transfer elements such as elements 12 and 16 of FIG. 2) with a coolant supplied to the outer elements whereby the lengths of the two edges of the steel band are then reduced and due to the tension which arises the layer of chips in the .area of its edges is pressed more strongly against the peripheral surface of the pressing drum 7. Consequently, a more uniform thickness of the chipboard over its complete cross-section is obtained.

If the edge regions of the chipboard produced has a lesser, thickness than the central area thereof then the respective outer edge elements of those provided would be supplied with a heating medium in order to increase the length of the steel band in its edge regions.

If it is found that the central area of the chipboard 9 is thinner than the two edge regions, this can also be caused by a deformation of the pressing drum surface. As a result of the heat supplied to the pressing drum surface the central area can bulge slightly outwards which can be compensated by lowering the temperature in the central elements and optionally increasing the temperature in the outer elements which serve to heat the pressing drum. The heat supply or heat reduction for the various elements can be continuously controlled by controller C in response to the measured thickness (measured by thickness sensing element S) of the produced chipboard 9 in accordance with a further feature of the invention.

Thickness sensing elements S and control devices C, C for effecting changes in the temperature of the respective heating/cooling elements of conventional construction can be used to practice the invention. One skilled in the art will be able to practice the invention with such known, sensing elements and control devices, given the present disclosure. For example, a plurality of separate thickness sensing elements S could be disposed to measure the thickness of the board 9 at different points across the width of the board 9. A control device C is provided for accepting the thickness signals from sensing elements Sand for sending appropriate control signals to raise or lower the temperature of respective ones of said heating and/or cooling elements in response to predetermined deviations from a constant thickness across the width of the board. This control device C is to be appropriately designed to effect the above-described heating and cooling sequence at the edge and central heat transfer elements in response to the respective prescribed thickness variations across the width of the board 9. This control arrangement is also to be appropriately connected to the elements in openings 29 and the electrical contacts of the elements shown in FIG. 3 (see schematically depicted control device C).

In order tobe able to influence the two edge regions of the pressing drum surface in a more precise manner, openings 29 are provided peripherally and uniformly in the side walls 27 and 28 of the pressing drum 7 in which for example. are placed electrically heatable elements. The invention contemplates embodiments where the heating of all the elements takes place gradually and embodiments where, for example, each second or third element is switched off. Since control means for switching on and off said electrically heatable elements of known constructions could be used by one skilled in the art, given the present disclosure, a further description thereof is dispensed with herein.

The heat transfer elements positioned along the travel path of band 1 between the rollers can be electrically actuable or they can be actuable in response to flow therethrough of appropriately heated or cooled fluid mediums such as steam, water, or oil.

While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. Apparatus for the continuous production of boards such as chipboards, fibreboards and the like; said apparatus comprising:

an endless band,

pressing means,

guiding and moving means for guiding and moving said band with a surface of said band in facing relationship to a pressing surface of said pressing means over a material pressing portion of the travel path of said band such that material forming said boards can be conveyed by and compressed between said band and said pressing surface along said material pressing portion, plurality of heat transfer elements disposed adjacent portions of the travel path of said band, said heat transfer elements being spaced from one another in a direction transverse to the travel path of said band, and temperature control means for maintaining said elements at different temperatures with respect to one another for accommodating transfer of different heat levels between the respective elements and respective width portions of the band.

2. Apparatus according to claim 1, wherein said temperature control means includes means for controlling the temperature of each of said heat transfer elements such that the temperature of said band is substantially constant across the width of the band when the band is disposed along said material pressing portions, whereby material forming said boards is compressed along said material pressing portion to substantially the same thickness over the entire width of the boards in a direction transverse to the travel path of said band.

3. Apparatus according to claim 1, wherein said pressing means is a rotatable pressing drum.

4. Apparatus according to claim 1, wherein said endless band is a steel band.

5. Apparatus according to claim 2, wherein said pressing means is a rotatable pressing drum.

6. Apparatus according to claim 5, wherein said endless band is a steel band.

7. Apparatus according to claim 3, wherein said guiding and moving means include guide and feed rollers, wherein said plurality of heat transfer elements includes a plurality of heat transfer elements extending circumferentially of at least one of said pressing drum and said rollers, said lastmentioned heat transfer elements being spaced from one another in a direction transverse to the travel path of said band for accommo dating transfer of different heat levels between the respective elements and respective width portions of the respective drum and rollers.

8. Apparatus according to claim 7, wherein said temperature control means includes means for controlling the temperature of each of said heat transfer elements such that the temperature of said band is substantially constant across the width of the band when the band is disposed along said material pressing portions, whereby material forming said boards is compressed along said material pressing portion to substantially the same thickness over the entire width of the boards in a direction transverse to the travel path of said band.

9. Apparatus according to claim 3, wherein said guiding and moving means includes guide rollers spaced substantially from said pressing drum and feed rollers immediately adjacent said pressing drum, and wherein said heat transfer elements include a plurality of heat transfer elements positioned adjacent said band travel path between said guide and feed rollers.

10. Apparatus according to claim 9, further comprising a forming station for supplying material for said boards to said band at a position between said guide and feed rollers, said forming station being disposed on the side of said band opposite said last-mentioned plurality of heat transfer elements.

11. Apparatus according to claim 3, wherein said pressing drum is shaped as a rotatable cylinder with the pressing surface formed on the cylindrical outward facing walls thereof and with side walls closing off the respective ends of the cylinder, and wherein heat transfer elements are disposed inside said drum in openings formed in said walls for accommodating heating of said side walls.

12. Apparatus according to claim 11, wherein the number of heating elements in said side walls is larger adjacent the cylindrical outward facing walls than in the area of the axis of rotation of the drum.

13. Apparatus according to claim 8, wherein said last-mentioned heat transfer elements are electrically actuable and extend circumferentially of said pressing drum and are connected via separate wires to respective different electrical slide contacts.

14. Apparatus according to claim 2, wherein each of said heat transfer elements include one of steam, water and oil actuable elements.

15. Apparatus according to claim 2, wherein said heat transfer elements include both cooling and heating elements.

16. Apparatus according to claim 2, wherein said temperature control means includes means for cooling the heat transfer elements in the area of the edge portions of said band to a lower temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that excess thickness of edge portions of the boards is reduced.

17. Apparatus according to claim 2, wherein said temperature control means includes means for heating the heat transfer elements in the area of the edge portions of said band to a higher temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that the thickness of the edge portions of the boards is increased.

18. Apparatus according to claim 16, wherein said temperature control means includes means'for heating the heat transfer elements in the area of the edge portions of said band to a higher temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that the thickness of the edge portions of the boards is increased.

19. Apparatus according to claim 2, wherein said temperature control means includes means for selectively switching heat supply to each transfer element.

20. Apparatus according to claim 2, wherein said temperature control means includes means responsive to the detected thickness along various width portions of the boards exiting from said material pressing portion for varying the temperature of the respective heat transfer elements.

21. Apparatus according to claim 20, wherein said temperature control means includes means for cooling the heat transfer elements in the area of the edge portions of said band to a lower temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that excess thickness of edge portions of the boards is reduced.

22. Apparatus according to claim 20, wherein said temperature control means includes means for heating the heat transfer elements in the area of the edge portions of said band to a higher temperature than the adjacent heat transfer elements in the area of the middle widthportions of the band so that the thickness of the edge portions of the boards is increased.

23. Apparatus according to claim 8, wherein said guide and feed rollers include:

a first guide roller positioned above and immediately downstream of the press drum with respect to the travelpath of said band,

a second guide roller spaced downstream of said first guide roller at the same level as said press drum,

a third guide roller spaced downstream of said secnd guide roller and immediately below said press drum to also serve as a feed roller,

a fourth guide roller spaced downstream of said third guide roller at a level slightly above the bottom of said press drum,

and a further feed roller spaced downstream of said fourth guide roller and immediately upstream of and adjacent to the lower part of said press drum.

24. Apparatus according to claim 23, wherein said material pressing portion of the travel path of said band extends over more than half the circumference of said press drum from said further feed roller to adjacent said first guide roller, and wherein a forming station is provided for introducing board material to said band at a position between said fourth guide roller and said further feed roller.

25. Apparatus according to claim 24, wherein a plurality of said heat transfer elements are arranged in side-by-side relationship between said fourth guide roller and said further feed roller and at the side of said band facing away from said forming station.

26. Apparatus according to claim 25, wherein a plurality of said heat transfer elements are arranged in side-by-side relationship at both sides of said band and between said first and second. said second and third. and said third and fourth guide rollers.

27. Apparatus according to claim 26, wherein a plurality of said heat transfer elements are arranged in side-by-side relationship adjacent to said band in facing relationship to the outer surface of said press drum.

28. Apparatus according to claim 27, wherein said temperature control means includes means for separately controlling the temperature of the various heat transfer elements so as to effect an effective control of the temperature gradient across the width of said band with a resultant optimization of the thickness control for the boards being produced.

29. Apparatus according to claim 1, wherein said heat transfer elements are arranged parallel to one another and extend parallel to the travel path of said endless band.

30. Apparatus for the continuous production of boards such as chipboards, fibreboards and the like; said apparatus comprising:

first pressing means,

second pressing means,

guiding and moving means for guiding and moving said first pressing means with a surface of said first pressing means in facing relationship to a pressing surface of said second pressing means over a material pressing portion of the travel path of said first pressing means such that material forming said boards can be conveyed by and compressed between said first and second pressing means along said material pressing portion, A plurality of heat transfer elements disposed adjacent portions of the travel path of said first pressing means, said heat transfer elements being spaced from one another in a direction transverse to the travel path of said first pressing'means,

and temperature control means for maintaining said elements at different temperatures with respect to one another for accommodating transfer of different heat levels between the respective elements and respective width portions of the first pressing .means. i

31. Apparatus according to claim 30, wherein said temperature control means includes means for controlling the temperature of each of said heat transfer elements such that the temperature of said first pressing means is substantially constant across the width of the first pressing means when the first pressing means is disposed along said material pressing portion, whereby material forming said boards is compressed along said material pressing portion to substantially the same thickness over the entire width of the boards in a direction transverse to the travel path of said band.

32. Apparatus according to claim 31, wherein said temperature control means includes means for heating the heat transfer elements in the area of the edge portions of said first pressing means to a higher temperature than the adjacent heat transfer elements in the area of the middle width portions of the first pressing means so that the thickness of the edge portions of the boards is increased. 

1. Apparatus for the continuous production of boards such as chipboards, fibreboards and the like; said apparatus comprising: an endless band, pressing means, guiding and moving means for guiding and moving said band with a surface of said band in facing relationship to a pressing surface of said pressing means over a material pressing portion of the travel path of said band such that material forming said boards can be conveyed by and compressed between said band and said pressing surface along said material pressing portion, a plurality of heat transfer elements disposed adjacent portions of the travel path of said band, said heat transfer elements being spaced from one another in a direction transverse to the travel path of said band, and temperature control means for maintaining said elements at different temperatures with respect to one another for accommodating transfer of different heat levels between the respective elements and respective width portions of the band.
 2. Apparatus according to claim 1, wherein said temperature control means includes means for controlling the temperature of each of said heat transfer elements such that the temperature of said band is substantially constant across the width of the band when the band is disposed along said material pressing portions, whereby material forming said boards is compressed along said material pressing portion to substantially the same thickness over the entire width of the boards in a direction transverse to the travel path of said band.
 3. Apparatus according to claim 1, wherein said pressing means is a rotatable pressing drum.
 4. Apparatus according to claim 1, wherein said endless band is a steel band.
 5. Apparatus according to claim 2, wherein said pressing means is a rotatable pressing drum.
 6. Apparatus according to claim 5, wherein said endless band is a steel band.
 7. Apparatus according to claim 3, wherein said guiding and moving means include guide and feed rollers, wherein said plurality of heat transfer elements includes a plurality of heat transfer elements extending circumferentially of at least one of said pressing drum and said rollers, said lastmentioned heat transfer elements being spaced from one another in a direction transverse to the travel path of said band for accommodating transfer of different heat levels between the respective elements and respective width portions of the respective drum and rollers.
 8. Apparatus according to claim 7, wherein said temperature control means includes means for controlling the temperature of each of said heat transfer elements such that the temperature of said band is substantially constant across the width of the band when the band is disposed along said material pressing portions, whereby material forming said boards is compressed along said material pressing portion to substantially the same thickness over the entire width of the boards in a direction transverse to the travel path of said band.
 9. Apparatus according to claim 3, wherein said guiding and moving means includes guide rollers spaced substantially from said pressing drum and feed rollers immediately adjacent said pressing drum, and wherein said heat transfer elements include a plUrality of heat transfer elements positioned adjacent said band travel path between said guide and feed rollers.
 10. Apparatus according to claim 9, further comprising a forming station for supplying material for said boards to said band at a position between said guide and feed rollers, said forming station being disposed on the side of said band opposite said last-mentioned plurality of heat transfer elements.
 11. Apparatus according to claim 3, wherein said pressing drum is shaped as a rotatable cylinder with the pressing surface formed on the cylindrical outward facing walls thereof and with side walls closing off the respective ends of the cylinder, and wherein heat transfer elements are disposed inside said drum in openings formed in said walls for accommodating heating of said side walls.
 12. Apparatus according to claim 11, wherein the number of heating elements in said side walls is larger adjacent the cylindrical outward facing walls than in the area of the axis of rotation of the drum.
 13. Apparatus according to claim 8, wherein said last-mentioned heat transfer elements are electrically actuable and extend circumferentially of said pressing drum and are connected via separate wires to respective different electrical slide contacts.
 14. Apparatus according to claim 2, wherein each of said heat transfer elements include one of steam, water and oil actuable elements.
 15. Apparatus according to claim 2, wherein said heat transfer elements include both cooling and heating elements.
 16. Apparatus according to claim 2, wherein said temperature control means includes means for cooling the heat transfer elements in the area of the edge portions of said band to a lower temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that excess thickness of edge portions of the boards is reduced.
 17. Apparatus according to claim 2, wherein said temperature control means includes means for heating the heat transfer elements in the area of the edge portions of said band to a higher temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that the thickness of the edge portions of the boards is increased.
 18. Apparatus according to claim 16, wherein said temperature control means includes means for heating the heat transfer elements in the area of the edge portions of said band to a higher temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that the thickness of the edge portions of the boards is increased.
 19. Apparatus according to claim 2, wherein said temperature control means includes means for selectively switching heat supply to each transfer element.
 20. Apparatus according to claim 2, wherein said temperature control means includes means responsive to the detected thickness along various width portions of the boards exiting from said material pressing portion for varying the temperature of the respective heat transfer elements.
 21. Apparatus according to claim 20, wherein said temperature control means includes means for cooling the heat transfer elements in the area of the edge portions of said band to a lower temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that excess thickness of edge portions of the boards is reduced.
 22. Apparatus according to claim 20, wherein said temperature control means includes means for heating the heat transfer elements in the area of the edge portions of said band to a higher temperature than the adjacent heat transfer elements in the area of the middle width portions of the band so that the thickness of the edge portions of the boards is increased.
 23. Apparatus according to claim 8, wherein said guide and feed rollers include: a first guide roller positioned above and immediately downstream of the press drum with respect to the travel path of said band, a second guide rolleR spaced downstream of said first guide roller at the same level as said press drum, a third guide roller spaced downstream of said second guide roller and immediately below said press drum to also serve as a feed roller, a fourth guide roller spaced downstream of said third guide roller at a level slightly above the bottom of said press drum, and a further feed roller spaced downstream of said fourth guide roller and immediately upstream of and adjacent to the lower part of said press drum.
 24. Apparatus according to claim 23, wherein said material pressing portion of the travel path of said band extends over more than half the circumference of said press drum from said further feed roller to adjacent said first guide roller, and wherein a forming station is provided for introducing board material to said band at a position between said fourth guide roller and said further feed roller.
 25. Apparatus according to claim 24, wherein a plurality of said heat transfer elements are arranged in side-by-side relationship between said fourth guide roller and said further feed roller and at the side of said band facing away from said forming station.
 26. Apparatus according to claim 25, wherein a plurality of said heat transfer elements are arranged in side-by-side relationship at both sides of said band and between said first and second, said second and third, and said third and fourth guide rollers.
 27. Apparatus according to claim 26, wherein a plurality of said heat transfer elements are arranged in side-by-side relationship adjacent to said band in facing relationship to the outer surface of said press drum.
 28. Apparatus according to claim 27, wherein said temperature control means includes means for separately controlling the temperature of the various heat transfer elements so as to effect an effective control of the temperature gradient across the width of said band with a resultant optimization of the thickness control for the boards being produced.
 29. Apparatus according to claim 1, wherein said heat transfer elements are arranged parallel to one another and extend parallel to the travel path of said endless band.
 30. Apparatus for the continuous production of boards such as chipboards, fibreboards and the like; said apparatus comprising: first pressing means, second pressing means, guiding and moving means for guiding and moving said first pressing means with a surface of said first pressing means in facing relationship to a pressing surface of said second pressing means over a material pressing portion of the travel path of said first pressing means such that material forming said boards can be conveyed by and compressed between said first and second pressing means along said material pressing portion, a plurality of heat transfer elements disposed adjacent portions of the travel path of said first pressing means, said heat transfer elements being spaced from one another in a direction transverse to the travel path of said first pressing means, and temperature control means for maintaining said elements at different temperatures with respect to one another for accommodating transfer of different heat levels between the respective elements and respective width portions of the first pressing means.
 31. Apparatus according to claim 30, wherein said temperature control means includes means for controlling the temperature of each of said heat transfer elements such that the temperature of said first pressing means is substantially constant across the width of the first pressing means when the first pressing means is disposed along said material pressing portion, whereby material forming said boards is compressed along said material pressing portion to substantially the same thickness over the entire width of the boards in a direction transverse to the travel path of said band.
 32. Apparatus according to claim 31, wherein said temperature control means includes means for heating the heat transfer elements in tHe area of the edge portions of said first pressing means to a higher temperature than the adjacent heat transfer elements in the area of the middle width portions of the first pressing means so that the thickness of the edge portions of the boards is increased. 